Project : Halloween boo badge

Discussion in 'The Completed Projects Collection' started by k7elp60, Oct 5, 2013.

  1. k7elp60

    Thread Starter Senior Member

    Nov 4, 2008
    478
    69
    This is a project I created several years ago and thought the members of this forum would enjoy it.
    It is personal badge that is the same size as a normal business card that has the letters BOO that flashes and is powered by a CR2032 coin size lithium battery. It uses a pair of CMOS 555 timers. The one driving the PN2222 transistor has a flash rate of approximately 14mS. The other timer adjust the flash rate from less than a 10th of a scond to a little over 3 seconds. When the LED’s appear on they are in fact flashing, but the eye sees them continually on.

    The circuit board is shown from the top of the board so it will have to be reversed on the bottom of the board. The switch shown in the picture is different from the parts list, as I used a sample I had in my stock.
    The circuit board pattern will have to be adjusted for the switch shown in the parts list. The parts list switch has 3 terminals, only two are connected to the circuit.

    The LED’s that I used are clear but illuminate in RED.
    This is a parts list of the specific parts:
    1. Battery Holder Renata, Mouser 614-HU2032-LF
    2. On/Off switch, Alco, Mouser 506-SLS211RA04
    3. 1M miniature trim pot,Vishay Mouser 72-T63ZB-1M
    4. 555 CMOS TIMER, TI, Mouser 926-LMC555CN/NOPB
    5. 3.3uF Radial electrolytic, Nichicon, Mouser 647-UMA1V3R3MDA

    There are LED’s in each letter that are in parallel with one current limiting resistor. Schematic A(the first schematic posted) is a circuit to match the LED’s within 50mV of each other. On the circuit for the LED matcher the value of Rs is 620 ohms(Rs=2.5/ILED)
    On the circuit for the LED matcher the value of Rs is 620 ohms(Rs=2.5/ILED)
    I have 3 packages consisting of the CMOS 555'S, the new switch, the battery holder, and the miniature 3.3uF capacitor
    that I will sell for $5.00 US dollars to USA members, postage paid.


    The circuit board was home made.
     
    Last edited by a moderator: Oct 6, 2013
  2. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    Can you please explain the purpose of the schematic in attachment #5? It doesn't seem to be implemented in any way in your board. Is it for test purposes? You should clarify that.
     
  3. k7elp60

    Thread Starter Senior Member

    Nov 4, 2008
    478
    69
    I added this paragraph
    There are LED’s in each letter that are in parallel with one current limiting resistor. Schematic A(the first schematic posted) is a circuit to match the LED’s within 50mV of each other. On the circuit for the LED matcher the value of Rs is 620 ohms(Rs=2.5/ILED)
     
  4. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    I'd like to know more about your LED matching circuit. If I read the schematic correctly, the upper OpAmp, along with the PNP transistor form a constant current source that drives the LED under test. Since you have a constant current feeding into the LED, you can measure the Vf of the LEDs at the same operating point.
    But what is the function of the TIL431 package?

    About the use of the circuit; You simply test LED after LED, take notes of their Vfs and then try to select the closest ones, right? Is all that done to ensure that the LEDs shine with the same intensity? Is it reasonable to assume that LEDs from the same batch shine equally brightly given the same current?
     
  5. k7elp60

    Thread Starter Senior Member

    Nov 4, 2008
    478
    69
    The TIL431 is a constant voltage reference(2.5V), so the applied voltage to the LED matcher is somewhat variable. Yes the LED's are matched within about 50mV of each other. There are two groups of 5 LED's in parallel for the the letter B, and 4 groups of 4 LED's for the letters O. With the red LED's all the forward voltages are near 2V. Only the individual groups have to me matched as there is a separate resistor for each group.

    I forgot to mention, after the board was etched, tin plated and the holes drilled I sprayed the top of the board with some flat black paint.
    I also have some of the stick on badge clips that I will put in the packages of parts for those who want them.
     
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